Method of producing matrices for the electroforming of foraminous sheets



Patented June 23,1942

METHOD OF PRODUCING MATRICES FOR THE ELECTROFORMING F FORAMINOUS SHEETSEdward 0. Norris, Westport, Comm, assignor to,-

Edward 0. Norris, Inc., New York, N. Y., a corpcration of New YorkOriginal application October 6, 1939, Serial No. 298,216. Divided andthis application January 21, 1941, Serial No. 375,156 Y 3 Claims. (01.204-11) This application is a division of my pendin application Ser. No.298,216, filed October 6, 1939, Patent No. 2,250,436, July 22, 1941.

The invention relates to matrices adapted to be employed as a cathodefor the reception of a non-adherent electrolytic deposit in the form offoraminous sheet. The deposit-receiving surface of such a matrixcomprises a network of electrically conductive material or at least ofmaterial capable of receiving an electrolytic deposit, the spacesdelimited by said network being of electrically non-conductive materialor at least of material that will not receive an electrolytic deposit.In matrices of this character, the insulated areas are produced by firstcreating a multitude of pits or depressions in a metal surface and thenfilling the pits or depressions with "the insulating material, which maybe Bakelite, 'glass, enamel or other material having the property abovedescribed. --'The foregoing and various other methods of producing sucha matrix are described in my United States Patents Nos. 2,166,366,issued "July 18, 1939, and 2,166,367, issued July 18, 1939, and, as thedetails of the method are not involved in the invention, they will notbe further described. T In order that the ultimate foraminous sheet tobe produced shall be of as uniform construction as possible, includinghole size, hole shape, and land cross-sectional shape, I find that it isdesirable in the first place to produce what may be termed a skeletonscreen, which is subsequently built up by a second electroforming stepafter the skeleton has been removed from the matrix. However, by thesimple etching process employed in producing the pits, it is verydifiicult to control the width of the lands of the matrix when thiswidth gets to be very narrow, for the reason that in such cases thewalls of adjoining pits are often broken down, which of course renclersthe matrix useless. It is therefore the principal object of theinvention to produce a matrix having much narrower lands or depositingareas than is possible with a simple etching process.

Referring to the drawing,

Fig. 1 is a perspective view of a fragment of a copper plate providedwith a multitude of pi in its surface;

Fig. 2 is a plan view of an obverse of the plate I Fig. 3 is a view onthe line 3-3 of Fig. 2;

Fig. 4 is a view showing two successive steps in the process;

Fig. 4a is a detail view of a fragment of Fig. 4;

Fig. 5 is a view in section of a base matrix;

Fig. 6 is a view similar to, Fig. 5 showing the pits of the base matrixof Fig. 5 filled with insulating material.

It should be explained that the most practical use to which such amatrix is put is that of producing very fine screen-say, from thathaving fifty apertures to the linear inch to that having severalhundred. It is therefore not leasible to illustrate the matrix of myinvention ex: cept on a very exaggerated scale. Of course, it is also tobe appreciated that only a very small areaof an actual matrix can beshown.

In practicing the invention, I-prefer to employ a base matrix havingspecial characteristics that function to retain the fillings securelylocked in place in the pits. The construction which I prefer for thispurpose consists in so shaping the pits that, as viewed in verticalsection, they appear to be slightly undercut to provide inwardlyoverhanging edges. A suitable process of producing a matrix of thischaracter will now be described, reference first being made to Figs.1-6, inclusive.

Fig. 1 shows a'plate A which may be of any metal that lends itself tothe process as I will describe it, but which is preferably of copper,the surface being provided with the pits ll isolated from each other bythe walls l2, and it will be observed that the walls of each pit flareslightly outwardly as'they approach the surface of the plate. Such aplate can be produced by several already known methods, but for aspecific de scription of,.one method reference is again made to my twopatents above referred to. Briefly, an illustrative method consists infirst applying a light-sensitive film, for example of light-sensitizedphotographers glue, to the surface of the plate, and then photo-printinga reticulated pattern on the light-sensitive film by projecting lightupon it through a screen exhibiting a multitude of opaque dots arrangedin rows and columns. After sumcient exposure the film becomes hardenedwhere exposed to the light (1. e., the light passing through the screenbetween the dots) and the unexposed portions (1. e., Where the light isstopped of! by the dots) being easily removable by washing. Afterwashing, etching fiuid (e. g., ferric chloride) is applied to the plate,resulting in producing the pits I I where the copper surface is exposed.I r

An obverse of the pitted surface of the plate Just described which Iwill refer to as the "master plate is then made by electrolyticdeposition, the deposit being likewise preferably of copper. In orderthat the deposit shall be nonadherent, the surface of the master platemay be coated with a stripping fihn, for example a very thin film of asolution of carnauba wax in benzol. It is preferable that the solutionbe applied sparingly, although of course in sufficient quantity to coverthe surface, and that the plate be heated in order to result in equaland complete distribution, and removal of the excess. Bronze powder suchas is used by electrotypers may be then dusted over the waxed surface.Such a surface although conductive, is non-adherent to electrolyticdeposition, and the result of this operation is illustrated in Figs. 2and 3, the protuberances which are the obverse of the pits of the masterplate being indicated by the numeral l3 and the valleys which are theobverse of the lands M of the master plate being indicated by thenumeral l5.

After the plate of obverse pattern to that of the master plate (which Iwill indicateas a whole by the letter B) has been stripped from themaster plate, it is formed into the shape of a hollow cylinder and itsends joined by any convenient means, such as by solder l5a, theprotuberances being then located on the interior periphery of thecylinder. To clearly show this, it is possible to illustrate only asection of the cylinder in the region of the juncture. In point of fact,in the case of a cylinder of the curvature shown, protuberances would bealmost, and in some cases actually microscopically small. The hollowcylinder formed from' the plate 3 is in turn used as a matrix for theelectrolytic deposition of a third plate indicated as a whole by theletter C. First, however, a thin adherent deposit N3 of copper isapplied to the patterned surface of the I6 is then removed either bychemical action or by deplating electrolytically, resulting in the plateshown in Fig. 5. If the copper is to be removed chemically, it may bedone by subjecting it to the action of (e. g.)-

(l) A solution of potassium cyanide or preferably (2) a mixture ofchromic or sulphuric acid in water, suitable proportions being about asfollows:

Sulphuric acid lbs 2 Chronic acid lb 1 Water... gals 10 Neither, ofthese reagents will have any appreciable effect on the nickel if merelyenough time is allowed for the reaction to remove the copper. If removedby deplating, conventional methods may be employed, the entire plate ofFig. 4 being simply employed as an anode in an electrolytic copper bath.

The pits [9 of the plate C are then filled with Bakelite 20, cement orother substance electrically non-conductive or at least incapable ofreceiving an electrolytic deposit on its exposed surface. Bakelite ispreferred.

It will be observed that, by virtue of the fact that the walls of eachpit converge slightly as they approach the surface, the fittings aresecurely locked in place and the cylinder of Fig. 6 with its fillingsmay serve as a matrix for the electrolytic production of foraminoussheet like screen or other fabric of reticulated pattern.

It is obvious from the foregoing that an im'- portant thing in theselection of metals (besides other a high throwing power as aboveexplained.

plate B-by electrodeposition, and the result is that if this step becarried out under standard conditions of operation, the rate of growthin thickness of the deposit in the depths ofthe valleys I5 is slowerthan the rate of growth on more exposed portions of the protuberances;The effect produced is illustrated in detail in Fig. 4a, where, as maybe observed, the copper is considerably thicker in the regions I! and I1than it is at the bottoms of the valleys as indicated at- IB and I8. Thedeposition is carried out to a sufficient extent to cause the areasindicated by H and H to approach each other, the ultimate result beingthat the dimension a. is less than the dimension D, but-yet thedimension b is much smaller than could be produced by simply etchingpits in the original plate. The plate thus produced is illustrated inFig. 4.

The plate C, of a metal difierent from copper-- e. g., nickel-is nowdeposited by electrodeposition' on the copper surface IS on the interiorof the periphery of the cylinder. -While it might appear that thenickel, like the copper, would grow in thickness more rapidly in theregions l1. l1 than in the regions 18, I find that such is not the caseand that the valleys become completely filled with nickel. I am not ableto explainthis phenomenon except by the theory that it is due to thehigh throwing power of nickel, The plate B with it added copper filmNickel and copper have these contrasting properties but are noted merelyby way of example,

although it may be said that thus far I have found that they answer mypurposes more satisfactorily than any other combination.

I have described above certain embodiments of my invention and apreferred process with certain modifications thereof, but I wish it tobe understood that these are illustrative and not limitative of myinvention and that I reserve the right to make various changes in form,construction, and arrangement of parts and also to make various changesin process of manufacture falling within the spirit and scope of myinvention, as set forth in the claims.

I claim:

1. In the method of producing a matrix for the electroforming offoraminous sheet with very narrow lands, the steps which compriseproducing a multitude of pits in the surface of a metal plate, renderingthe pitted surface including the surfaces of the pits capableofreceiving an electrolytic deposit that is non-adherent thereto,producing from the said plate by electrodeposition a second metal platewith a surface that is the obverse of the pitted surface of thefirst-mentioned plate, building out the resulting protuberances on thesaid second plate laterally by electrodeposition to partially overhangand narrow the valleys that separate them, electroforming on the saidsecond plate a third plate which is the electroforming of foraminoussheet with very narrow lands, which comprises producing a multitude ofpitsin the surface of a metal plate,

rendering the pitted surface including the surfaces of the pits capableof receiving an electrolytic deposit that is non-adherent thereto, pro--ducing from the said plate a second plate with a surface that is theobverse of the pitted surface of the first-mentioned plate, building outthe resulting protuberances on the said second plate laterally topartially overhang and narrow the valleys that separate them,elect'roforming on the.

said secondplate a third plate, then removing the second plate from thethird plate, and filling the pits in the third plate with materialpassive to electrolytic deposition.

3. In the method of producing a matrix for the electroforming offoraminous sheet with very narrow lands, the steps which compriseproducing a metal plate from the surface of which a multitude ofprotuberances having electrically from the electroformed plate, andfilling the pits in the electroformed plate which are the obverseof theprotuberances with material passive to electrodeposition.

EDWARD O. NORRIS.

